# Questions tagged [thermodynamics]

Covers the study of (mostly homogeneous) macroscopic systems from a heat/energy/entropy point of view. Consider also using tag: [statistical-mechanics].

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### When are Dufour and Soret effects non-negligible?

Dufour effect is often times excluded from energy equations without mentioning. But there are many papers (out of my iq-league) which study effects of these phenomena in chemically reacting flows. ...
267 views

### Fan and venturi effect

A simple calculation shows the power $P$ you can get from wind at speed $v$ passing through an area $A$ is (in Watts) $$P = 1.23\,v^3 \frac{A}{2}.$$ Using the above equation and taking the Venturi ...
1 vote
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### Using Helmholtz Free Energy to Calculate Liquid Density

My objective is to find an equation of state (EoS) for density, i.e. density as a function of pressure, temperature and concentration, for aqueous acids, bases and salts. A StackExchange user ...
94 views

### What is the temperature of vacuum?

I wonder what the temperature of vacuum is. Is it the absolute zero？ The vacuum is defined without taking into account the Unruh effect or the CMB，it is just vacuum with nothing in it but quantum ...
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### What is the entropy associated with a diffusion process?

Is it possible to calculate entropy from the solution of a diffusion equation(with natural boundary conditions) by using the formula of Shanon entropy? Could anyone help me to understand the entropic ...
8k views

### How can I understand a Vortex Tube and its efficiency?

A Vortex Tube takes a pressurized input stream, most typically of a gas, and creates two output streams with a temperature differential. Apparently, it has been described as a Maxwell's Demon. Both ...
159 views

### Do liquids in tall containers or wide containers cool faster?

Given two containers of equal volume, one tall and thin, one short and wide, containing the same liquid at the same temperature, pressure, etc... which one would cool faster?
1 vote
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### Statics and dynamics in elasticity : how to add time in elasticity

In elasticity, there is are static relations of the form $R(\sigma,\epsilon)=0$. In fluid dynamics, there is a dynamics relation with the conservation of momentum leading to Navier-Stokes equation. ...
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### If our planet had more gravitational force would rain clouds still form? [closed]

If the air pressure on Earth at sea level were 25 psi (about 172.000 Pascals), would rain clouds still form?
1 vote
47 views

### Entropy vs dimension of the Hilbert space

In the definition of thermodynamic entropy $S=k\ln\Omega$ where $\Omega$ is the number of possible microstates of a given macrostate, we can also associate $\Omega$ with the dimension of the Hilbert ...
759 views

### Why does symmetry reduce heat capacity?

For monatomic gasses, the heat capacity approaches $3R/2$ because there are three degrees of freedom (DOF) of translational motion. For diatomic gasses it approaches $7R/2$ because the symmetry about ...
24 views

### Water in house to heat and cool? [closed]

In the summer, when it reaches 27c during the day I want it to be colder, and when it reaches 15c at night I want it to be warmer. Is it possible to do some of this heating and cooling with water (...
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1 vote
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### Predicting the effect of a power outage on the temperature in my fridge

I have a commercial fridge, without a freezer. It is vertical fridge with one glass door. We have medications we want to keep below 8°C. Most medication tolerate a slight T elevation without problem. ...
2k views

### Why are thermodynamic potentials minimised?

Why is it that, at equilibrium, certain potentials are minimised? That is, for a system at constant temperature and pressure, the Gibbs free energy is minimised, and for fixed volume and temperature, ...
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### Is it possible to define concepts like free energy in the diffusion process?

How does the idea of free energy (which we derive from the canonical partition function) fit in the domain of non-equilibrium processes like diffusion?
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